Theorem 1 ([1]}) 
Let \(\phi : \mathbb {R}^d \rightarrow \mathbb {R}^{2D}\)  be a nonlinear transformation:
\(\phi \left({\mathbf {x}}\right) = \sqrt{1/D}\Bigl [\sin \left({\mathbf {w}}_1\cdot {\mathbf {x}}\right),\dots ,\sin \left({\mathbf {w}}_D\cdot {\mathbf {x}}\right),\cos \left({\mathbf {w}}_1\cdot {\mathbf {x}}\right),\dots ,\cos \left({\mathbf {w}}_D\cdot {\mathbf {x}}\right)\Bigr ]^\top .\) 
